1. Field of the Invention
The present invention relates to the redistribution of an incident density profile of light to yield a new desired intensity profile and, in one application, the concentration of the light into a new desired intensity profile for irradiating particles.
2. Description of the Prior Art
Many prior art flow cytometers utilize a laser beam for irradiating particles, suspended in a fluid flow, to produce detectably optical signals. These flow cytometers waste much of the high cost, high grade incident light. Typically, beam shaping optics focus collimated light from the laser into a slit-like ellipse at the location where the particles are illuminated. In that it is necessary to irradiate the particles with a relatively uniform high intensity light across the range of possible particle trajectories, only a relatively small center portion of this incident light usually is used, as shown in FIG. 5, by the range of (-a.ltoreq.x.ltoreq.+a), wherein a equals the limiting x coordinate value for a particle trajectory. The unused energy (i.e., wasted) in the wings of this slit can be 84% of the total energy for a 2% variation in intensity across the possible particle trajectories, assuming a Gaussian intensity profile along the x direction of FIG. 5. If a smaller amount of variation in intensity is required (e.g., 1%), a higher percentage of incident energy is not used.
Accordingly, it can readily be seen that there is a need in the art of cytology for a cytometer that utilizes more of the available radiant energy, while at the same time, maintains negligible or low intensity variations across the possible particle trajectories. For more generalized usage, there is a need in the optical arts for transforming organized incident radiation into radiation having a desired intensity profile.
Relevant prior art is disclosed in U.S. Pat. No. 3,476,463 to Kreuzer; U.S. Pat. No. 4,128,308 to McNaney; Data Sheet No. 512, January, 1978, of Spawr Optical Research, Inc.; and Fluorescence Techniques in Cell Biology, A. A. Thaer and M. Sernetz, Springer-Verlag, 1973, p. 80.